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From: Peter Otten <__peter__@web.de>
Newsgroups: comp.lang.python
Subject: Re: ignoring or replacing white lines in a diff
Date: Thu, 14 Jan 2016 22:05:48 +0100
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Xref: csiph.com comp.lang.python:101716

Adriaan Renting wrote:

> 
> Maybe someone here has a clue what is going wrong here? Any help is
> appreciated.
> 
> I'm writing a regression test for a module that generates XML.
> 
> I'm using diff to compare the results with a pregenerated one from an
> earlier version.
> 
> I'm running into two problems:
> 
> The diff doesn't seem to behave properly with the -B option. (diff (GNU
> diffutils) 2.8.1 on OSX 10.9)
> 
> Replacing -B with -I '^[[:space:]]*$' fixes it on the command line,
> which should be exactly the same according to:
> http://www.gnu.org/software/diffutils/manual/html_node/Blank-Lines.html#Blank-Lines
> 
> (for Python problem continue below)
> 
> MacRenting 21:00-159> diff -w -B test.xml xml/Ticket_6923.xml
> 3,5c3,5
> <   <version>2.15.0</version>
> <   <template version="2.15.0" author="Alwin de Jong,Adriaan Renting"
> changedBy="Adriaan Renting">
> <   <description>XML Template generator version 2.15.0</description>
> ---
>>           <version>2.6.0</version>
>>           <template version="2.6.0" author="Alwin de Jong"
> changedBy="Alwin de Jong">
>>           <description>XML Template generator version
> 2.6.0</description>
> 113d112
> <
> 163d161
> <
> 213d210
> <
> 258d254
> <
> 369d364
> <
> 419d413
> <
> 469d462
> <
> 514d506
> <
> 625d616
> <
> 675d665
> <
> 725d714
> <
> 770d758
> <
> 881d868
> <
> 931d917
> <
> 981d966
> <
> 1026d1010
> <
> 1137d1120
> <
> 1187d1169
> <
> 1237d1218
> <
> 1282d1262
> <
> 
> /Users/renting/src/CEP4-DevelopClusterModel-Story-Task8432-
SAS/XML_generator/test
> MacRenting 21:00-160> diff -w -I '^[[:space:]]*$' test.xml
> xml/Ticket_6923.xml
> 3,5c3,5
> <   <version>2.15.0</version>
> <   <template version="2.15.0" author="Alwin de Jong,Adriaan Renting"
> changedBy="Adriaan Renting">
> <   <description>XML Template generator version 2.15.0</description>
> ---
>>           <version>2.6.0</version>
>>           <template version="2.6.0" author="Alwin de Jong"
> changedBy="Alwin de Jong">
>>           <description>XML Template generator version
> 2.6.0</description>
> 
> 
> Now I try to use this in Python:
> 
>       cmd   = ["diff", "-w", "-I '^[[:space:]]*$'", "./xml/%s.xml" %
> name, "test.xml"]

Instead of 

..., "-I '^[[:space:]]*$'", ...

try two separate arguments

..., "-I", "^[[:space:]]*$", ...

>       ## -w ignores differences in whitespace
>       ## -I '^[[:space:]]*$' because -B doesn't work for blank lines
> (on OSX?)
>       p     = subprocess.Popen(cmd, stdin=open('/dev/null'),
> stdout=subprocess.PIPE, stderr=subprocess.PIPE)

I don't think you need to specify stdin.

>       logs  = p.communicate()
>       diffs = logs[0].splitlines() #stdout
>       print "diff reply was %i lines long" % len(diffs)
> 
> This doesn't work. I've tried escaping the various bits, like the * and
> $, even though with single quotes that should not be needed.
> 
> I tried first removing the blank lines from the file:
> 
>       import fileinput
>       for line in fileinput.FileInput("test.xml",inplace=1):
>         if line.rstrip():
>           print line
> 
> This makes it worse, as it adds and empty line for each line in the
> file.

Add a trailing comma to suppress the newline:

print line,

> I've tried various other options. The only thing I can think of, is
> ditching Python and trying to rewrite the whole script in Bash.
> (It's quite complicated, as it loops over various things and does some
> pretty output in between and I'm not very fluent in Bash)
> 
> Any suggestions?

Whatever floats your boat ;)